Preparation of 2,3-dimethylbutane



June 19, 1951 R. M. KENNEDY ErAL PREPARATION oF 2,5-D1ME'mYLBUTANE FiledSept. 15, 1948 R SY TE E NN N .O EN H Y Wg MM.. l R .V MM w mzm on. +6 Tm H mona..." M m M Nm R y V B mzganrbmism N mN\\ QN/ m. V| S mZEmmOn.NN\1 wn A mozxw A aux.: E52 hdm: 0N

S 1A..- mzFSmom. .Vl ll; .Q n t S QN mooa mzmJrfFm omm on. mzomn \.mm nGWV. zo ....FnE n m .I mlm C/ /Q lllv IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIlllll l. .V lllllllllllllll I 4 lllllllllllllllllllll I wzbmom.

Patented June 19, 1951 PREPARATION OF 2,3-DIMETHYLBUTANE Robert M.Kennedy, Newtown Square, and Abraham Schneider, Philadelphia, Pa.,assignors to Sun Oil Company, Philadelphia, Pa., a corporation of NewJersey Application September 15, 1948, Serial No. 49,447

(Cl. Zim-683.4)

10 Claims.

ploying certain catalysts. Diisopropyl has become increasingly importantin recent years as an additive for the preparation of high quality fuelsfor spark ignition engines due to its high antiknock qualities and goodvolatility. It has a high octane rating and excellent rich-mixtureresponse, which render it especially useful for preparing high qualityaviationfuels.

The catalysts which have been proposed heretofore for carrying out thealkylation of isobutane and ethylene include aluminum chloride with apromoter such as HC1, BFa-HzO- Ni complexes and BFamO- HIE complexes.These catalytic materials are insoluble in hydrocarbons or at leastsoluble only to a limited extent. When such catalysts are employed inconducting the reaction, it is thereforer necessary to effect intimatecontact between the hydrocarbon phase and the catalyst phase, andusually a mechanically agitated reactor is provided for continuously.agitating the reactants and catalyst during the reaction period. Thisadds considerably to the expense of the operation with respect both toinstallation charges and operating costs.

According to the present invention, the alkylation of isobutane andethylene is carried out under novel catalytic conditions such that thereaction is elected in homogeneous phase. The components constitutingthe catalyst are an alkyl fluoride and BFJ. Each of these are soluble inthe reactants at least in the concentrations employed, so that thereaction does not depend upon contact between two separate phases.

The process of the invention comprises bringing together an alkylfluoride and BF: in the presence of isobutane and ethylene at a suitabletemperature as hereinafter' morefully set forth, whereby a catalyticcondition becomes estab-- lished that causes the alkylation reaction totake= place immediately. In bringing together the alkyl iluoride andBFs, the alkyl fluoride can be introduced into a mixturel of thereactants to which BF; has already been added, or the BF3 can beintroduced into a solution of the alkyl fluoride in the reactants, orboth of the catalytic components can be introduced simultaneously butseparately into the reactants. It is also permissible first to dissolveone of the catalytic components in either the isobutane or ethylene andthe other in the other reactant and then bring together the separatemixtures to effect reaction. It is not permissible, however, to premixthe alkyl fluoride and BFs and then add the mixture to the hydrocarbons,for in such case the catalytic condition Will be immediately spent whenthe alkyl fluoride and BFa are brought into contact with each other.

The alkyl fluoride employed should have at least two carbon atoms permolecule. It may be a primary fluoride (i. e. one having the iluorineatom attached to a primary carbonatom), a secondary fluoride (i. e.where the fluorine atom is attached to a secondary carbon atom) or atertiary fluoride (i. e. where the fluorine atom is attached to atertiary carbon atom). Any primary, secondary or tertiary alkylfluoride, other than methyl fluoride, is operative in combination withBF3 to promate the alkylation of isobutane and ethylene-to form2,3-dimethy1butane.

The temperature at which such reaction will `be obtained varies,however, with the particular alkyl iluoride employed; We have found thatwhen the fluoride is a tertiary fluoride, the temperature should be inexcess of 20 C. At lower temperatures, while a reaction will take place,it will comprise largely the reaction of ethylene with the tertiaryfluoride to form a primary fluoride of higher molecular weight, with thealkylation reaction between isobutane and ethylene proceeding only to aminor extent.

When the alkyl fluoride is a secondary uoride, the temperature should bein excess of C. At temperatures below this value, a secondary fluoridein combination with BFs has little catalytic effect. At temperatureshigher than 90 C., the alkylation of isobutane with ethylene will takeplace without any substantial reaction of the fluoride with ethylene asoccurs in the case when a tertiary fluoride is employed at temperaturesbelow 20 C.

When the alkyl fluoride is a primary fluoride, the reaction temperatureshould be above 10 C. in order to obtain substantial catalytic action.Ethyl fluoride, however, has been found to be somewhat more inert thanthe primary fluorides `having three or more carbon atoms per moleculeand requires a. temperature of at least about +20 C, in order to giverise to substantial catalytic action. Methyl fluoride in combinationwith BF3 does not give any substantial catalytic effect at least attemperatures below C. and is not considered within the scope of thepresent invention.

The reaction may, if desired, be carried out at much higher temperaturesthan the minimum values above specified, ad no definite maximumtemperature can be given for all cases. In prac- Vtice the maximumtemperature which may be employed usually will depend upon the pressureunder which the available equipment is adapted to operate or upon thedesired degree of purity of the 2,3-dimethylbutane. As a general rule,it will be desirable to operate at all times at temperatures below +l50C. and usually well below this value. 'It is noteworthy, however, thatthe use of the present type of catalytic agents permits theisobutane-ethylene alkylation to be conconducted over a much wider rangeof temperatures than are employed in the known processes using othercatalysts.

As specific examples of primary uorides which may be used in practicingthe process, the following may be mentioned by way of illustration:

ilo

ethyl fluoride; n-propyl uoride; n-butyl iluoride; isobutyl duoride;n-amyl fluoride; isoamyl fluoride; 1-fluoro-2-methylbutane; n-hexylnuoride; and similar fluoride derivatives of hexanes, heptanes, octanesor the like. As specific illustrations of secondary fluorides, thefollowing may be mentioned: isopropyl fluoride; 2-iiuoro-butane;3,3-dimethylbutane. A few specific examples oi' tertiary uorldes are:t-butyl uoride; t-amyl uoride; 2iiuoro-2,3dimethylbutane and othert-hexyl fiuorides; t-heptyl iluorides; and4-iiuoro-2,2-4-trimethylpentane and other t-octyl fluorides. It will beunderstood that the specific compounds named above are given merely byway of illustration and that any alkyl uoride (with the exception ofmethyl iiuoride) will produce an operative catalytic combination withBF3 provided the temperature is above the minimum values as set forthabove.

In alkylation processes generally, some reaction other than straightalkylation of the isoparaflin with the olen invariably occur along withthe main alkylation reaction. 'I'his is also true of alkylationsconducted according to the present process. Accordingly, the -totalreaction `product contains other hydrocarbons in addition to the Ceproduct of the isobutane-ethylene alkylation. A relatively small amountof C'z hydrocarbons and a considerably larger amount of Ca hydrocarbonsare formed. Also the product contains a considerable amount of C andheavier hydrocarbons. However, these other products of the reaction arealso isoparafllns of highly branched structure and are likewise usefulfor preparing high quality fuels. Where it is desired to obtain the2,3-dimethylbutane in high concentration, it

may be separated from the other hydrocarbons by distillation. On theother hand, where it is not desired to separate the 2,3-dimethy1butane,the total hydrocarbon product or so much thereof as has a suitableboiling range may be used directly for the manufacture of aviation orother motor fuels.

It is noteworthy that the total Cc fraction of the reaction product ofthe present process is composed mainly of 2,3-dimethylbutane and in ymany cases, especially when the reaction is conducted at relatively lowtemperature. will consist essentially of 2,3-dimethylbutanesubstantially free of any of its isomers. This is advantageous in thatit readily permits the separation of the 2,3-dimethy1butane from theother hydrocarbon products in an unusually high state of purity. By wayof contrast, heretofore known processes for allwlating isobutane withethylene generally yield the 2,3-dimethylbutane in admixture withsubstantial amounts 4 of other hexanes of inferior antiknock value.

The accompanying drawing is a diagrammatic now-sheet illustrating onemanner of conducting the process.

Referring now to the now-sheet, isobutane enters the system through lineI0 and is passed through line I I wherein it is mixed with ethylenewhich is introduced through line I2. The proportion of isobutane toethylene may vary widely but it is generally desirable to use a molarexcess of theisobutane in order to minimize polymerization of theethylene. Onv the other hand, as the concentration of isobutane in thereaction mixture is increased, there is a tendency to promoteself-alkylation of the isobutane, or in other words to cause theisobutane to react with itself to form Ca hydrocarbons. and it istherefore desirable to avoid the use of isobutane in such highproportions as to cause the self-alkylation reaction to predominate overthe isobutaneethylene alkylation. Molar proportions of isobutane toethylene varying from 1:1 to 8:1 are suitable, although the process mayalso be practiced with lower or higher proportions.

The mixture of isobutane and ethylene flows through heat exchanger Il,which may be either a cooler or heater dependent upon the temperature atwhich it is desired'to conduct the reaction. The reactants, at thedesired temperature, leave the exchanger I3 through line I4 and are thenmixed first with one of the catalytic components and then with theother. For purpose of illustration, the BF; is considered as thecatalytic componentwhich is added to the reactants rst. following whichthe alkyl uoride is introduced into the BFE-containing mixture; but itis to be understood that the reverse order of addition also may be used.Also, in the acccmpanying drawing, the alkyl uoride is illustrated asisopropyl fluoride, although any other alkyl iiuoride as hereinpreviously speciiied can be used in place of isopropyl uoride.

BF; is introduced through line I5 into the reactant stream iiowingthrough line Il and mixes therewith in mixer I6 to form a solution ofBF: in the hydrocarbons. It will be apparent that if there is suilicientturbulence in line I 4 to eiect rapid mixing, mixer I6 may be omitted.The amount of BF: to employ is not critical and a very small amount issuiilcient, upon the subsequent addition of the alkyl fluoride, toestablish the necessary catalytic condition.

After the addition of BFa, the alkyl iiuoride, shown as isopropylfluoride, is introduced through line I1 into the BF'a-hydrocarbonmixture flowing throughline I8. It is desirable to add a suilicientproportion of the alkyl fluoride to eifect complete consumption of theethylene during the reaction. This amount will be subject to variationdepenaent upon other operating conditions but generally will be inexcess of 0.05 mole of alkyl fluoride per mole of ethylene charged. Itis seldom if evexl advantageous to employ a proportion in excess of 1.0mole per mole of ethylene unless it is desired also to etl'ectself-alkylation of the excess isobutane.

A catalytic condition becomes established inimediately upon contact ofthe isopropyl iiuoride and BFa, and reaction of the hydrocarbonsstartevr -'becomes heterogeneous due to separation of a sludge from thehydrocarbon phase. A stream of the reaction mixture may be continuouslywithdrawn from mixer Il and sentl through line 2l into separator 22wherein separation of the two phases is allowed to occur. The sludgesettles to the bottom of the separator and is withdrawn through line 23.This material contains iluorine derived from the alkyl fluoride togetherwith BF: in some sort of complex form. If desired, means (not shown) maybe provided for recovering BF: from the sludge and re-using the same.This .'may be done, for example, by heating the sludge to drive oif BF:and HF and then recovering the BF: from the evolved vapors by fractionaldistillation.

The hydrocarbon product is withdrawn from separator 22 through line 24and is sent to distillation zone 25 for separation of the components.Distillation z'one 25 usually will comprise a plurality of separatedistillation steps suitable for making the separations indicated. Thelowest boiling component will be the BFa which has re mained dissolvedin the hydrocarbon layer. As indicated, this may be withdrawn throughline 26 and may be returned for re-use through line 21.

As shown in the drawing, propane is the next lower boiling constituentobtained from the reaction mixture and is removed through line 28. Thiscompound is formed during the reaction from the isopropyl fluoride. Ithas been found that the alkyl fluoride employed will be converted, atleast in part, during the reaction to the corresponding hydrocarbon.Consequently, if an alkyl fluoride other than isopropyl fluoride isused, some vother hydrocarbon will be obtained rather than propane. Forexample, if tertiary butyl fluoride is used. it will be converted toisobutane and no provision for removal of propane need be made in suchcase. f The excess isobutane may be separated by distillation andwithdrawn through line 29, whence it may be returned by means of line 30for re-use.

As a general rule, a. relatively small amount of isopentane will beproduced, evidently through disproportionation of the isobutane with Ceor higher boiling hydrocarbon products of the reaction. As shown,provision may be made for removing the isopentane through line 3 I Thenext higher boiling material is the Cs product which is removed throughline 32. As previously indicated, the Cs fraction is composed at leastmainly of 2,3-dimethylbutane and in fact may be substantially pure2,3-dimethylhutane. Low reaction temperature favors high purity. It hasbeen found that at temperatures below +20 C., the Cs fraction usually iscomposed essentially of 2,3-dimethylbutane without any substantialamount of its isomers. On the other hand. at a temperature of, forexample, +100 C., the Cs fraction will contain a substantial proportionof 2-methylpentane, which compoundl has considerably lower antiknockqualities than 2,3-dimethylcia-ag cglut the reaction at a temperaturebelow The remainder of the reaction product, which is withdrawn throughline 33, is composed of C1 and higher boiling isoparaiiins. This productalso has utility in the preparation of aviation or vother motor fuels.

The following examples illustrate specific embodiments of the invention:

Example I 'Ihree runs (A, B and C) were made at diiierent Vtemperatures(0 C.. 20 C. and 100 C. respectively) using isopropyl iluoride as thealkyl fluoride in each run. The procedure was first to charge theisobutane, ethylene and isopropyl fluoride into a contactor providedwith stirrer and then introducing BF: by bubbling it into the mixture.After introduction of the BF: a period of contact of about 45-60 minuteswas allowed during which the mixture was stirred, but froml observationof pressure variations within the contactor it was apparent that thereaction in each case took place immediately upon addition of the BFs.Upon standing the reaction mixture separated into an organic layer and adark lower layer containing BF: in a complex form. The

frared analysis. Results are summarized as follows:

Bun A Run B Run C Reaction temperature. C 0 2) 100 Charge:

isobutane, g 223 221 225 eth ene. g Si 3l 48 isopropyl fluoride, g. l 2122 l0 l0 l0 leid of s+ product, g... 37 57 85 leid of C-| product. g...36 57 82 Comlo tion of Cg+ product, voi. per cent:

s 13 21 28 C1 6 8 l1 Cl Zi 19 18 C; and heavier 58 52 43 Composition of0| fraction, vol. per cent:

2,3-dimethylbutane 99 75 2-methylpenhme 1 25 These results indicate thatwhile the yield of Cs product increases as the reaction temperatureincreases, its purity with respect to 2,3-dimethylbutane decreases.

Example II 00 In this example isopropyl-fluoride was again first toremove any components boiling below the Ca range and then to removeisopentane formed butane. It will therefore often vbe desirable to 1|during the reaction. The residue was then sub- Jected to distillationunder high fractionating conditions. vThe following results wereobtained:

It is noteworthy that under the conditions of this run, not only was theCs fraction essentially pure 2,3-dimethylbutane as in run A of thepreceding example but the yield of 2,3-dimethylbutane based on theamount of ethylene charged was considerably higher than in run A.

Example III In this example a tertiary alkyl iluoride, namely, tertiarybutyl iluoride, was employed at a temperature of C., using the techniqueof-slowly adding the alkyl fluoride (44 g.) dissolved in a.

portion (58 g.) oi' the isobutane to the other components over a periodof about 42 minutes. Results were as follows:

Composition of Ce fraction, vol. per cent:

2,3-dimethylbutane 100 Here, again, a relatively good yield ofessentially pure 2,3-dimethylbutane was obtained.

It will be understood that the foregoing examples are merelyillustrative speciiic embodiments of the invention and that widedeviation from the specic reaction conditions therein shown arepermissible.

This application is a continuation-impart of our copending application,Serial No. 38,167, illed July 10, 1948.

Having described our invention, what we claim and desire to protect byLetters Patent is:

1. Method of preparing 2,3-dimethylbutane by the instantaneousalkylation in homogeneous phase of isobutane with ethylene whichcomprises reacting isobutane and ethylene in the presence of a. catalystcomprising an admixture of BFE and an alkyl iluoride having at least twocarbon atoms per molecule at a. temperature suilicient to eil'ect said`instantaneous homogeneous phase reaction,

Reaction temperature, "C 0 Charge:

Isobutane, g 204 Ethylene, a 19 BFa. s 4 6 Tertiary butyl fluoride, g 44Yield of C5| product, g 70 Yield of Cs+ product, g 63 Composition of Cs+product, vol. per cent:

C9 and heavier 31 8... said temperature being in the C. to 150 C.

2. Method according to claim 1 wherein there is separated from thereaction product a Cs iraction composed mainly of 2,3-dimethylbutane.

3. Method of preparing 2,3-dimethylbutane by the instantaneousalkylation in homogeneous phase of isobutane with ethylene whichcomprises reacting isobutane and ethylene in the presence of a catalystcomprising an admixture of BF: and a tertiary alkyl fluoride at atemperature sufficient to effect said instantaneous homogeneous phasereaction. said temperature being in the range of from 20 C. to 150 C.

4. Methodaccording to claim 3 wherein the alkyl fluoride is tertiarybutyl fluoride'and the molar ratio of isobutane to ethylene is withinthe rangeof1:1to8:1.

5. Method of preparing 2,3-dimethylbutane by the instantaneousalkylation in homogeneous phase of isobutane with ethylene whichcomprises reacting isobutane and ethylene in the presence of a catalystcomprising an admixture of BF: and a secondary alkyl fluoride at atemperature sufficient to eiect said' instantaneous homogeneous phasereaction, said temperature being in the range oi' from 90 C. to 150 C.

6. Method according to claim 5 wherein the alkyl fluoride is isopropylfluoride and the molar ratio of isobutane to ethylene is within therange of 1: 1 to 8: 1. I

7. Method of preparing 2,3-dimethylbutane by the instantaneousalkylation' in homogeneous phase of isobutane with ethylene` whichcomprises reacting isobutane and ethylene in the presence of a catalystcomprising an admixture of. BF3 and a primary alkyl iluoride having atleast 3 carbon atoms per molecule at a temperature suilicient to eiectsaid instantaneous homogeneous phase reaction, said temperature being inthe range ofy from 10 C. to 150 C.

8. Method of preparing 2,3-dimethylbutane by the instantaneousalkylation in homogeneous range of from phase of isobutane with ethylenewhich comprises introducing an alkyl iluoride having at least two carbonatoms per molecule into a mixture of isobutane and ethylene containingdissolved BF.; at a temperature sufficient to eiect said instantaneoushomogeneous phase reaction, said temperature being in the range of from90 C. to 150 C.

9. Method according to claim 8 wherein alkyl fluoride is tertiary butyluoride.

10. Method according to claim 8 wherein the alkyl iluoride is isopropylfluoride.

ROBERT M. KENNEDY. ABRAHAM REFERENCES CITED The following references areof record in the ille of this patent:

UNITED STATES PATENTS the Number Name Date 2,304,290 Van Peski Dec. 8,1942 2,366,736 Linn et al. Jan. 9, 1945 2,410,108 Sachanen et al Oct.29, 1946 2,411,483 Wachter et al Nov. 19, 1946

1. METHOD OF PREPARING 2,3-DIMETHYLBUTANE BY THE INSTANTANEOUSALKYLATION IN HOMOGENEOUS PHASE OF ISOBUTANE WITH ETHYLENE WHICHCOMPRISES REACTING ISOBUTANE AND ETHYLENE IN THE PRESENCE OF A CATALYSTCOMPRISING AN ADMIXTURE OF BF3 AND AN ALKYL FLUORIDE HAVING AT LEAST TWOCARBON ATOMS PER MOLECULE AT A TEMPERATURE SUFFICIENT TO EFFECT SAIDINSTANTANEOUS HOMOGENEOUS PHASE REACTION, SAID TEMPERATURE BEING IN THERANGE OF FROM -90* C. TO 150* C.